The invention relates to a device for edge-machining of an optical lens. In particular, the invention relates to a CNC-controlled device, suitable for industrial use, for edge-machining of spectacle lenses, which allows spectacle lenses to be finish-machined at the edges even in relatively large numbers with the necessary precision in very short machining times.
Where the term spectacle lenses is used below, it should be understood to mean optical lenses or lens blanks for spectacles made of the usual materials, such as polycarbonate, inorganic glass, CR-39, HI-Index etc., and with circumferential edges of any shape, which lenses or lens blanks may be, but do not have to be, machined on one or both optically effective surfaces prior to machining of the edge thereof.
In the field of spectacle lens edge machining, the aim of which is to finish-machine the edge of a spectacle lens in such a way that the spectacle lens may be inserted into a spectacle frame, a trend has recently begun to emerge for this demanding machining to be relocated away from the opticians"" workshops to the spectacle lens manufacturers in particular for reasons of rationalisation. When carried out by the spectacle lens manufacturers, this procedure requires spectacle lens machining machines, also known as xe2x80x9cedgersxe2x80x9d, which may quickly edge-machine the widest possible range of spectacle lenses with the required precision without much effort being required for setting up and may be used reliably for long periods.
In the prior art, there is no shortage of proposals for speeding up the edge-machining of spectacle lenses. For instance, the generic EP-A-0 917 929 discloses an edger for spectacle lenses which, to increase efficiency during machining, comprises two tool posts which are arranged parallel to the vertically extending axis of rotation of the spectacle lens to be edge-machined and are each provided with a set of grinding wheels. The one set of grinding wheels comprises a rough-grinding wheel and an intermediate grinding wheel provided with various grooves for beveling, while the other set of grinding wheels comprises a similar rough-grinding wheel and a finish-grinding wheel provided with beveling grooves for finishing. For each tool post there is provided an (X-Z) compound slide arrangement, with a vertical slide and a horizontal slide. On one side, the vertical slide is guided displaceably in the vertical direction on a machine frame while, on the other side of the vertical slide, the horizontal slide is guided displaceably in the horizontal direction. On the side remote from the vertical slide, the horizontal slide bears the respective tool post. By means of CNC-controlled slide drives, each tool set may be moved in a radial direction relative to the spectacle lens to be machined and parallel to the axis of rotation of the spectacle lens. The spectacle lens to be machined is clamped between two coaxial spectacle lens holding shafts, of which the lower spectacle lens holding shaft is arranged stationarily while the upper spectacle lens holding shaft can be moved relative to the lower spectacle lens holding shaft only in the direction of the workpiece axis. Finally, a CNC-controlled rotary actuator is provided for each spectacle lens holding shaft, such that the previously known edger is controlled in altogether 6 CNC axes. The rotary actuators are CNC-coupled for simultaneous rotation of the spectacle lens to be machined.
A spectacle lens edge grinding machine has also been proposed for speeding up edge-machining of spectacle lens (U.S. Pat. No. 4,179,851, DE-A-34 18 329), which, reversing the above conditions, has a grinding wheel set which is rotatable about a horizontally extending axis of rotation but is otherwise stationary. Moreover, this machine comprises two pairs of coaxial spectacle lens holding shafts for simultaneous edge-machining of two spectacle lenses, which holding shafts are oriented parallel to the axis of rotation of the tool. An (X-Y) cross slide arrangement is associated therein with each pair of spectacle lens holding shafts, such that the respective spectacle lens clamped between the spectacle lens holding shafts and to be edge-machined may be moved in the radial direction relative to the grinding wheel set and parallel to the axis of rotation of the grinding wheel set.
Finally, DE-U-298 23 464 discloses a concept in which a conventional machining machine for shaping the left spectacle lens and a further conventional machining machine for shaping the right spectacle lens are linked together via a conveying means and a handling apparatus for accelerated production of the left and right spectacle lenses for a spectacle frame.
Edge-machining of spectacle lenses may in principle indeed be speeded up with the above-described known methods. However, for industrial use, in which it is also necessary to machine relatively large numbers over relatively long periods without problems arising with regard to machining quality, the known methods appear to be suitable to only a very limited extent, in particular with respect to their mechanical structure.
For the sake of completeness, it should also be mentioned in this context that the prior art also includes proposals to provide an additional tool on a spectacle lens edger, which tool serves to form channels on the periphery of the shaped spectacle lens or bores or grooves in the spectacle lens and/or to bevel or chamfer the edges of the spectacle lens. This additional tool renders it unnecessary to transfer the spectacle lens to or reclamp it in a further machining machine and in this respect also speeds up edge-machining. In this context, methods are known in which (1) the additional tool is stationary with regard to the main tool, which may be moved in two mutually perpendicular directions by means of a compound slide arrangement, and is driven by the rotary actuator of the main tool (DE-A-43 08 800), (2) the additional tool may be swiveled relative to a stationary main tool from a rest position into a machining position, in order to enter into drive connection with the main tool and into machining engagement with the spectacle lens (EP-A-0 820 837), as are methods in which (3) the additional tool, provided with its own rotary actuator, may be swiveled relative to a stationary main tool from a rest position into a machining position, in order to come into machining engagement with the spectacle lens (DE-A-198 34 748).
The object of the invention is to provide a device of the simplest possible, compact construction for edge-machining an optical lens, in particular a spectacle lens, which meets industrial requirements with regard to throughput and machining quality.
According to one aspect of the present invention, there is provided a device for edge-machining an optical lens, which may be clamped between two aligned holding shafts rotatable about a rotational axis of a workpiece, having a first slide, which is guided longitudinally displaceably on a base frame in a first direction parallel to the rotational axis of the workpiece, and a second slide bearing a tool post with an edge-machining tool for the optical lens, which slide is guided longitudinally displaceably on the first slide in a second direction perpendicular to the first direction in such a way that the edge-machining tool may be brought into machining engagement with the optical lens; wherein the base frame is of substantially O-shaped construction and surrounds the first slide, and wherein the first slide is likewise of substantially O-shaped construction and surrounds the second slide. In other words, the slides are nested telescopically inside one another relative to one another and to the base frame, respectively, in an open rectangular frame construction.
According to a second aspect of the present invention, there is provided a device for edge-machining an optical lens, which may be clamped between two aligned holding shafts rotatable about a rotational axis of a workpiece, having a first slide, which is guided longitudinally displaceably on a base frame in a first direction parallel to the rotational axis of the workpiece, and a second slide bearing a tool post with an edge-machining tool for the optical lens, which slide is guided longitudinally displaceably on the first slide in a second direction perpendicular to the first direction in such a way that the edge-machining tool may be brought into machining engagement with the optical lens; wherein an additional machining means is fixed to the second slide, which means comprises at least one further edge-machining tool for the optical lens, which is movable from a parked position into a machining position between the optical lens and the edge-machining tool on the tool post.
In the case of a device for edge-machining an optical lens, in particular a spectacle lens, which may be clamped between two aligned holding shafts rotatable about the rotational axis of a workpiece, having a first slide, which is guided longitudinally displaceably on a base frame in a first direction parallel to the rotational axis of the workpiece, and a second slide bearing a tool post with an edge-machining tool for the optical lens, which is guided longitudinally displaceably on the first slide in a second direction perpendicular to the first direction in such a way that the edge-machining tool may be brought into machining engagement with the optical lens, the base frame is of substantially O-shaped construction and surrounds the first slide, wherein the first slide is likewise of substantially O-shaped construction and surrounds the second slide.
Together with a compact construction, such a device exhibits very high rigidity due to the closed force flow established by the O-shaped construction of the base frame, which rigidity allows higher speeds and acceleration rates to be achieved during adjustment movements and, where technologically possible, also during feed movements than was possible with conventional edgers. Tests performed by the applicant have shown that the times necessary for edge-machining are significantly reduced by the construction of the device according to the invention relative to the previously known edgers using comparable edge-machining tools (grinding wheels, milling cutters or combinations thereof) and thus productivity may be markedly increased without this being detrimental to machining quality. Even in the case of extended use, as is usual with industrial manufacture, a uniformly good machining quality is achieved, because the O-shaped construction of the base frame and the first slide likewise ensures thermal symmetry, in which the thermal expansions caused by heating up of the drive and machining components involved are mutually compensated.
Embodiments of the edge-machining device are disclosed which are advantageous especially from the point of view of thermally invariable behaviour. For instance, a linear guide for the first slide may be provided on each side of the base frame, wherein the linear guides extend parallel to one another on the base frame. Each linear guide for the first slide may comprise a guide rail attached to the base frame and two guide shoes engaging with the guide rail, which guide shoes are fixed to the first slide in symmetrical arrangement. A linear guide for the second slide may be provided on each side of the first slide, wherein the linear guides extend parallel to one another on the first slide. Finally, each linear guide for the second slide may comprise a guide rail attached to the first slide and two guide shoes engaging with the guide rail, which guide shoes are fixed to the second slide in symmetrical arrangement.
The first slide and/or the second slide is preferably movable by means of a hollow shaft servo motor, which comprises a rotatable nut, which is in active engagement with a non-rotatable ball screw. This embodiment of the device advantageously allows further optimisation of the speeds and acceleration rates of the adjustment and feed movements, together at the same time with good linear positioning accuracy and reduced structural space requirements relative to known designs with additional transmission elements, such as drive belts or clutches. This optimisation potential during adjustment and feed movements is primarily attributable to the fact that the non-rotatable arrangement of the ball screw, which renders unnecessary the end bearings which are necessary with rotating spindles and limit axial force, ensures increased axial rigidity and elevated torsional rigidity of the ball screw. In addition, the problem of critical whirling speeds does not arise with a non-rotatable ball screw. All in all, higher speeds and acceleration rates are possible.
The hollow shaft servo motor for the first slide may be attached to the base frame, while the ball screw is preferably attached non-rotatably and centrally on the first slide. This has the advantage on the one hand that the hollow shaft servo motor, which is thus stationary, does not have also to be accelerated or braked during adjustment and feed movements. On the other hand, the central position of the ball screw on the first slide advantageously ensures that no tilting moments are introduced into the first slide, which could inter alia be detrimental to the smooth running of the adjustment movement. The same is true of an arrangement, according to which the hollow shaft servo motor for the second slide is preferably attached centrally to the second slide, while the ball screw is attached non-rotatably to a yoke plate, which is connected firmly to the first slide.
The ball screw interacting with the hollow shaft servo motor for the second slide may exhibit a large pitch in relation to conventional screw pitches, which amount to approximately 5 mm, said large pitch being between 20 and 35 mm, more preferably between 25 and 30 mm. The gear action obtained from this large ball screw pitch allows the peripheral edge of the spectacle lens requiring machining to be machined quickly and without risk of breakage or damage of the spectacle lens, wherein, due to the slight axial force applicable via the ball screw to the second slide, slippage of the spectacle lens clamped between the holding shafts during machining is also reliably prevented. Such slippage must not occur for example under any circumstances if the spectacle lens to be machined comprises a close-focus portion aligned in angularly precise manner relative to the optical axis or a cylindrical or prismatic ground surface, the axial position of which must be in a predetermined relationship to the position of the spectacle lens mounted in the spectacle frame. In addition to this feed movement precision during machining, which is beneficial to control of the machining process, the gear action of the large ball screw pitch has the additional advantage that the adjustment movements of the second slide may proceed very quickly.
The tool post with the edge-machining tool may be appropriately located in the working chamber, which is separated from the axis system by means of a sliding member surrounding the second slide and rolling lobe or expansion bellows, which are arranged between the sliding member and the tool post. These separating measures are advantageously beneficial to the smooth-running of the adjustment and feed movements.
The first direction may extend vertically, while the second direction may extend horizontally. The vertical arrangement of the holding shafts for the optical lens to be machined, which is due to the parallelism between first direction and rotational workpiece axis, has the advantage that automatic loading of the device may be more readily managed by means of suitable handling apparatus, as would appropriately be provided in industrial manufacture.
A weight counterbalancing means is advantageously provided for weight counterbalancing for the slides, one end of which means is preferably supported centrally on the base frame while another end thereof is preferably connected centrally with the first slide. On the basis of this embodiment, the drive for the first slide does not therefore have to lift or hold the entire weight of the slides and the components attached thereto, which is advantageous particularly with regard to the maximum possible speeds and acceleration rates of the vertical movements. The central arrangement of the weight counterbalancing means relative to the base frame or the first slide also advantageously prevents the introduction of tilting movements into the first slide, which could be detrimental to the smooth-running of the vertical movements. The weight counterbalancing means used may be for example a pneumatic cylinder, which may be selectively pressurized by means of a pressure regulator, or a spring element. As an alternative to this embodiment, a counterweight for the slide with corresponding force deflection by means of a lever, for example, would also be feasible; such an embodiment is less preferable, however, than a purely linearly acting weight counterbalancing means due to the greater structural space requirements and because of the greater masses moved.
According to a further aspect of the present invention, in the case of a device for edge-machining an optical lens, in particular a spectacle lens, which may be clamped between two aligned holding shafts rotatable about the rotational axis of a workpiece, having a first slide, which is guided longitudinally displaceably on a base frame in a first direction parallel to the rotational axis of the workpiece, and a second slide bearing a tool post with an edge-machining tool for the optical lens, which is guided longitudinally displaceably on the first slide in a second direction perpendicular to the first direction in such a way that the (first) edge-machining tool may be brought into machining engagement with the optical lens, an additional machining means is fixed to the second slide, which means comprises at least one further edge-machining tool for the optical lens, which may be moved from a parked position into a machining position between the optical lens and the (first) edge-machining tool on the tool post.
Depending on the design of the additional edge-machining tool, the additional machining means may, as a means complementary to the first edge-machining tool provided on the tool post, be used to perform further machining processes which may be necessary, such as the formation of bores or channels in a spectacle lens, without the optical lens having to be removed from its chucking arrangement, which again speeds up edge-machining. For this, the existing axis system encompassing the base frame and the slides is advantageously used, i.e. additional controlled axes for the further edge-machining tool and the associated costs are unnecessary. If machining of the optical lens is performed with the first edge-machining tool provided on the tool post, the further edge-machining tool is located in its parked position. For further machining of the optical lens with the additional edge-machining tool, the latter is moved from its parked position into its machining position, in which it is located between the optical lens and the first edge-machining tool on the tool post, i.e. upstream of the first edge-machining tool when viewed in the direction of machining feed, such that said first machining tool is not in the way during further machining. It will be appreciated that the adjustment and feed movements of the further edge-machining tool may be controlled like the movements of the first edge-machining tool, wherein only the distance between the first edge-machining tool and the further edge-machining tool need be taken into account from the point of view of control.
In an advantageous embodiment, the additional machining means may comprise its own housing, which is flange-mounted on the second slide. Due to this modular construction, the device may optionally be retrofitted without difficulty with the additional machining means.
The additional machining means may comprise a swivel mechanism, by means of which the further edge-machining tool may be swiveled from the parked position into the machining position. Such a swivel mechanism advantageously allows movement of the further edge-machining tool with only one degree of freedom into the space between the first edge-machining tool and the optical lens to be machined, i.e. movement of the further edge-machining tool about the first edge-machining tool. The swivel mechanism may appropriately have a swivel lever mounted on the housing and a simple linear swivel drive, which is coupled at one end to the housing and at its other end to the swivel lever, wherein the linear swivel drive is preferably a pneumatic cylinder.
The further edge-machining tool is driven rotationally about an axis of rotation by means of a rotary actuator, which is in particular independent of the rotary actuator of the first edge-machining tool. The rotating further edge-machining tool may here for example be a drill or end-milling cutter for forming bores or grooves in the edge area of a spectacle lens, these being required for securing the spectacle lens in a spectacle frame. Grinding wheels for forming roof-shaped bevels and/or safety bevels on the spectacle lens edge are conceivable, as are tools for forming channels or grooves at the peripheral edge of the spectacle lens, with geometrically indeterminate cutting edges, such as sintered diamond wheels, or geometrically determinate cutting edges, such as saw blades or side milling cutters. The axis of rotation of the additional edge-machining tool may appropriately extend parallel to the axis of rotation of the first edge-machining tool provided on the tool post.
The rotary actuator for the further edge-machining tool may be fixed to the swivel lever, which simplifies the transmission of torque to the further edge-machining tool, wherein the axis of rotation of the rotary actuator extends perpendicularly to the axis of rotation of the further edge-machining tool. The latter is beneficial to a compact structure, wherein deflection of the torque may proceed simply by means of a pair of bevel gears or a flexible shaft.
Finally, in an advantageous further development of the device, the additional machining means may have a tool holder driven rotationally by means of the rotary actuator, which holder comprises a first clamping mechanism for radial chucking of an edge-machining tool and a second clamping mechanism for axial clamping of at least one edge-machining tool. By providing these different clamping mechanisms, both drills or end-milling cutters, for example, may be radially chucked and grinding wheels, saw blades or side milling cutters, for example, optionally even in combination, may be axially chucked, such that the additional machining means may be equipped in accordance with the respective requirements of the intended edge-machining.
At this point, it should also be mentioned that the above-described construction of the device having a tool post for a first edge-machining tool and an additional machining means for at least one further edge-machining tool enables the most varied tool combinations and thus the performance of the most varied machining processes. For instance, a combined tool with a grooved milling cutter may be provided as first edge-machining tool for producing the peripheral contour of and optionally a roof-shaped bevel on a spectacle lens and a grinding wheel for polishing the spectacle lens periphery optionally provided with a roof-shaped bevel, while the additional machining means may be equipped, as described above, with tools for forming bores, grooves, channels and/or bevels in the edge area of the spectacle lens. It is also feasible to transfer production of the peripheral spectacle lens contour to the additional machining means, wherein laser or water jet cutting heads may be used as the additional edge-machining tool, which heads serve in particular to perform parting cuts for forming the peripheral contour. Beveling and polish-machining of the spectacle lens periphery and bevel formation could in this instance be performed by means of the first edge-machining tool. The device described herein is particularly attractive for industrial use not least because of this flexibility with regard to the tools which may be used and the processes which may be performed.